Contact chatter indicator



June 3, 1941. KREBS 2,244,338

CONTACT CHATTER INDICATOR Filed-Aug. so. 1940 l? 14 m REVERSING KEY W a"="20 9 P lNl ENTOR LE. KREBS Im-k dt Patented June 3, 1941 FFIE OONTACI' CHATTER INDICATOR Luther E. Krebs, West Orange, Bell Telephone Laboratories,

N. J., assignor to Incorporated, New

York, N. Y., a corporation of New York Application August 30, 1940, Serial No. 354,780

Claims.

This invention relates to apparatus for electrical testing and more particularly to apparatus for testing electric contacts for chattering.

Contact chattering very often takes place between a pair of contacts either when these contacts are in the process of closing or after they have been closed for some time due to mechanical vibration of either the contact closing mechanism itself or to the vibration of associated apparatus. Such chattering produces numerous undesirable effects among which are the generation of undesirable transients in associated circuits, the partial or complete failure of certain associated apparatus to operate and excessive burning of contacts where they carry heavy currents in inductive circuits. In testing electrical .circuits containing contacts and particularly when making is desirable to have apparatus which will quickly and reliably indicate the occurrence of chatte It is therefore the object of this invention to provide suitable means for quickly and reliably indicating the occurrence of contact chattering.

The foregoing object is attained by this invention by providing a gas-filled electron discharge device adapted to be responsive to the oscillatory discharge of a resonant circuit whose oscillations are started by the momentary opening of the contacts under test.

The invention may be better understood by referring to the drawing, in which: Fig. 1 discloses the preferred embodiment of the circuits of this invention;

Fig. 2 shows a simple pair of contacts which may be connected to Fig. 1 for chatter'test; and Fig. 3 is a schematic disclosure of a coin collector relay which may be connected to Fig. 1 for chatter test of the coin signal contacts.

Referring now to Fig. 1, a gas-filled electron discharge device I is specifically disclosed as a cold cathode-triode such as the Western Electric 333 A tube. Most any other type of gasfilled tube with either hot or cold cathode may be used provided it has at least some kind of control electrode and an anode. In Fig. 1 tube I contains an anode 2, a cathode 8 and control electrode 4. The oscillatory control circuit comprises inductor 5 and capacitor 6 connectedin parallel relationship. One side of this oscillatory circuit is connected by way of conductor I! through an obvious circuit including the reversing section II of reversing key 9 to the cathode 3 of tube I. A voltage divider comprising two resistors I3, I4 is connected in series relation routine tests of such circuits, it

rheostat I2, inductor 5 between cathode 3 and to the other side of the oscillatory circuit by way of key 1 and condenser 25. A tap on resistors l3, I4 is, connected to control electrode 4. by way of conductor I8. The purpose of condenser 25 will be described later.

A direct current source of voltage supply 8 is disclosed specifically in the form of a battery although obviously it may be any other form of direct current supply. An adjustable tap along the positive end of this voltage supply is connected to anode 2 of tube I via conductor I9, switch section III of reversing key 9, rheostat l5 and indicating lamp I 6. Terminals A and C are provided to furnish means for connection to the contacts under chatter test. Current supply for this test is obtained from battery I via conductors 20 and M, reversing section II oi. key 9,

and key I.

Fig. 2 discloses a simple pair of contacts 24 having terminals A and ,C'. It is assumed that these contacts are normally closed by some means not shown and that they are subject to chattering from any cause whatever. these contacts terminals A and C are connected to terminals A and C, respectively. of Fig. 1. Rheostat I5 is adjusted to properly limit the current for lamp I9, depending upon the voltage selected at battery 8 for the anode circuit and the type of gas-filled electron device employed. and rheostat I2 is adJusted for the proper test current through the contacts under test. Key 1 is operated to in and reversing key 9 may be operated either to left or right. Should the contacts 24 chatter when connected in the circuit, that is, should they momentarily open, the electromagnetic field included in coil 5 will suddenly collapse thereby setting up an oscillatory current between inductor 5 and capacitor 5. This will give rise to a relatively large altemating current voltage being generated across the terminals of inductor 5 which will be impressed across resistors I3 and I4. Since the test voltage selected by conductor I9 at source 8 is below the normal anode-cathode flash-over voltage tube I will normally remain deenergized. However, the higher oscillatory voltage generated in inductor 5 is sufficiently large that when its first positive cycle is impressed on terminal C it initiates a discharge of tube I byraising the potential of its control electrode 4 above the normal flash-over point. Tube I thereupon discharges and maintains its anode-cathode circuit fromsource 8 via conductor I9, key section III of reversing key 9. rheostat -I5, lamp I6 through the anode-cathode circuit of tube I and back In order to test I to source I via conductor 2|. This illuminates lamp It and indicates that chatter has taken place.

Many types. of gas-filled tubes will serve as suitable indicators by themselves and in these cases the use of a separate indicator lamp is is optional.

Should it be desired to observe the chatter efiects of the contacts when current is passed through them in a reverse direction, reversing key 9 may be operated in the opposite direction from that which it was operated for the first test whereupon a second test may be made of the contacts.

Fig. 3 discloses a schematic of a coin collector relay having terminals A, B" and C. It will be noted that here again the contacts 24 under test are connected between terminals A and C as in Fig. 2. In the coin collector relay these contacts are mechanically closed upon dropping the coin in the coin chute and should remain closed until after the coin collector relay armature 23 completes its operation to either collect or refund the deposited coin. It will be understood that the coin collector relay 22 is of the polarized type so that it will operate in one direction for one direction of current through its coil and in the other direction for the reverse direction'of current, thereupon effecting refund or collect at the will of the operator. Current for operating this relay is supplied through the coin signal contacts 24 by way of terminals A, B. In testing this relay its terminals A, B, C are connected to terminals A, B and C, respectively, of Fig. 1. Key 5 and capacitor 0 are switched out of the circuit. The coin collector relay does not ordinarily contain a capacitor across its coil terminal-l. However, the distributed capacitance thereof is sufficient to form a suitable resonant circuit equivalent to that formed by inductor I and capacitor 6, and to aid in understanding the invention stray capacitor 8' has been added to Fig. 3. The test is thereafter performed in the same manner as described for the simple contact of Fig. 2. Conductor 2| is adjusted to select a suitable voltage from battery I corresponding with the central ofilce voltage supplied for coin collector purposes. Rheostat I2 is adjusted to correspond with a representative line circuit impedance for coin collector circuits. The reversing section H of reversing key I provides a convenient means for reversing the direction of current through the windings of relay 2! to cause it to operate in either the collect or refund direction.

Condenser I! is provided to prevent false dis: charges of tube I when testing certain relays whose coils 22 have a low Q but operate on a high voltage. For most coils, however, this condenser may be omitted and resistor I! connected directly to terminal C.

Key section II of reversing key l provides a suitable means of unlocking the anode-cathode circuits of tube I after discharge thus restoring the tube to its deenergized condition. In order to prevent false indications upon the opening of key 9, the contacts of key section II are adjusted to open the anode circuit appreciably before the contacts of reversing section II open the circuit through the contacts under test.

It should be observed that gas tube I is responsive to the chattering of the contacts under test irrespective of the normal direct current polarity of terminals A and B. This is because 1 is switched to "out" whereupon inductor the direct current potential of these terminals is not used to discharge the tube but rather the oscillatory discharge voltage initiated by the mo mentary opening of the contacts under test whereby a higher alternating current voltage is induced across inductor i or the winding of coin collector relay 22. While this oscillatory voltage gradually decays due to the energy loss in its resistance component the circuit constants have nevertheless been so selected that the positive half cycle of the first whole cycle of alternating current will have a voltage suiilciently high to cause tube I to discharge.

As previously stated the chattering of the contacts disclosed in Fig. 2 may be caused by any kind of mechanical vibration. In the case of Fig. 3 the contacts are first normally closed by means of a coin dropped in the coin chute. Some of these coin collectors have an actual mechanical linkage between armature 23 and the coin collector contacts. Although this mechanical linkage is not designed to open these contacts upon the attraction of the armature to the pole faces of winding 22, the mechanical disturbance of this linkage at times will cause the coin collector contacts to chatter resulting in an unstandard condition. In so far as this invention is concerned however, it is unnecessary that any mechanical linkage actually exists between armature 23 and the coin collector contacts. All that is necessary is that the mechanical vibration or shock incident upon the operation of the coin collector relay or other auxiliary apparatus. be of suflicient magnitude and sufnciently proximate to the contacts under testes to tend to cause them to momentarily separate.

What is claimed is:

1. An apparatus for indicating contact chatter comprising a gas-filledelectron discharge device, an anode, a cathode, and a control electrode therefor, an inductor and a capacitor connected to form an oscillatory circuit, means connecting said oscillatory circuit to the cathode and control electrode to cause the electron discharge device to be responsive to oscillatory voltages of predetermined magnitude generated therein, a source of direct current voltage lower than the normal anode-cathode break-down voltage, means connecting said anode in series with the source and the cathode, terminals for connection to the contacts under test, means including the said terminals for connecting said source and said inductor in series relation with, the contactsunder test whereby oscillatory voltages of predetermined magnitudes are generated across said'coil :epzn a momentary opening of the contacts under 2. An apparatus for indicating contact chatter comprising a gas-tilled electron discharge device. an anode, a cathode, and a control electrode therefor, an inductor and a capacitor connected to form an oscillatory circuit, means connecting said oscillatory circuit to the cathode and control electrode to cause the electron discharge device to be responsive to oscillatory voltages of predetermined magnitude generated therein, a source of direct current voltage lower than the normal anode-cathode break-down voltage, means connecting said anode in series with the source and the cathode, terminals for connection to the contacts under test, means including the said terminals for connecting said source and said inductor in series relation'with the contacts under test, means for reversing the direction of direct current through the contacts under test whereby oscillatory voltages of predetermined magnitudes are generated across said coil upon the momentary opening or the contacts under test irrespective of the initial direction of direct current flowing through said contacts. 1

3. An apparatus for indicating contact chatter comprising a gas-filled electron discharge device, an anode, a cathode, and a control electrode therefor, an inductor and a capacitor connected to form an oscillatory circuit, means connecting said oscillatory circuit to the cathode and control electrode to cause the electron discharge-device to be responsive to oscillatory voltages of predetermined magnitude generated therein, a source oi direct current voltage lower than the normal anode-cathode break-down voltage, means connecting said anode in series with the source and the cathode, terminals for connection to the contacts under test, means including the said terminals and a current-reversing means for connecting said source and said inductor in series relation with the contacts under test, and circuitbreaking means included in the anode circuit and adapted to cooperate synchronously with said reversing means to open the anode circuit substantially before the reversing means opens the circuit to the contacts under test.

4. An apparatus for indicating contact chatter comprising a gas-filled electron discharge device, an anode, a cathode, and a control electrode therefor, an inductor and a capacitor connected to form an oscillatory circuit, means connecting said oscillatory circuit to the cathode and control electrode to cause the electron discharge devariable voltage 3 vice to be responsive to oscillatory voltages of predetermined magnitude source 01 direct current the normal anode-cathode break-down voltage, means connecting said anode in series with the source and the cathode, terminals for connection to the contacts under test, an impedance varying means, and means including the said voltage lower than terminals and said impedance varying means for connecting said source and said inductor in series relation with the contacts under test.

5. An apparatus for indicating contact chatter comprising a gas-filled electron discharge device. an anode, a cathode, and a control electrode therefor, an inductor and a capacitor connected to form an oscillatory circuit, means connecting said oscillatory circuit to the cathode and control electrode to cause the electron discharge device to be responsive to oscillatory voltages oi predetermined magnitude generated therein, a source of direct current voltage lower than the normal anode-cathode break-down voltage, means connecting said anode in series with the source and the cathode, terminals for connection to the contacts under test, means for obtaining a source of controlled magnitude from said direct current source, an impedance varying means, and means including said terminals and said variable impedance means for connecting said controlled voltage source and said inductor in series relation therewith and with the contacts under test.

LUTHER E. KREBS.

generated therein, a 

